Catalysts in liquid form have been used to produce polymers to control properties such as particle size distribution and flowability. Examples of liquid catalysts include, but are not limited to, metallocene catalysts and Ziegler-Natta catalysts. Other liquid catalysts include catalysts incorporating transition metals—Group IV, V, and VI metals—that have at least one π-bonded ligand.
Catalysts are injected as a liquid feed into a polymerization reaction to obtain better control over the reaction, to optimize the thermodynamics of the reaction, and to control the particle size distribution (PSD) of the polymers. PSD affects polymer properties such as flow characteristics of the polymer particles, the carbon black loading of the polymers, the ability to purge the polymer particles, the degree of segregation in packaging of the polymer, the amount of scrap generated, and the overall consistency of the polymer. Further, tails of the production, the fines and oversize particles, represent wasted material in the production of the polymers.
Particle size has been traditionally controlled by mechanical methods such as sieving. These methods are generally carried out after the polymers have been removed from the polymerization reactor.
U.S. Pat. No. 5,317,036 (Brady, III, et al.) describes gas-phase polymerization of olefins by using liquid catalysts. U.S. Pat. No. 5,693,727 (Goode, et al.) discloses controlling polymer PSD by spraying liquid catalysts into a zone that is polymer particle lean. The previously described processes control particle size by allowing a brief period of time for the droplets of liquid catalyst to disperse into the gas phase before contacting the polymer fluidization bed by using a purge gas to deflect polymer particles from the inlet catalyst stream.